Although that is changing slowly. PWAs are starting to get more and more support for APIs on the devices. For example if you install te Microsoft teams app, afaik it’s also just a web app, but bundled with all the rest so that it seems like a normal app.
PWA’s can even have hardware GPU support nowadays.
The way Reddit did this was by just giving out a token, that could be done in the same way here on lemmy, I think that would solve the issue.
Now it’s true that you will be redirected to the site (here lemmy) but that’s the same on all services, as a user one needs to check the host name and certificate of the site they’re directed to.
For me it’s Avatar the last airbender I just love how wholesome it is xD